Controls on Turbulent Mixing in a Strongly Stratified and Sheared Tidal River Plume

Joseph T. Jurisa, Jonathan D. Nash, James N. Moum, Levi F. Kilcher

Research output: Contribution to journalArticlepeer-review

19 Scopus Citations

Abstract

Considerable effort has been made to parameterize turbulent kinetic energy (TKE) dissipation rate ε and mixing in buoyant plumes and stratified shear flows. Here, a parameterization based on Kunze et al. is examined, which estimates ε as the amount of energy contained in an unstable shear layer (Ri < Ric) that must be dissipated to increase the Richardson number Ri = N2/S2 to a critical value Ric within a turbulent decay time scale. Observations from the tidal Columbia River plume are used to quantitatively assess the relevant parameters controlling ε over a range of tidal and river discharge forcings. Observed ε is found to be characterized by Kunze et al.'s form within a factor of 2, while exhibiting slightly decreased skill near Ri = Ric. Observed dissipation rates are compared to estimates from a constant interfacial drag formulation that neglects the direct effects of stratification. This is found to be appropriate in energetic regimes when the bulk-averaged Richardson number Rib is less than Ric/4. However, when Rib > Ric/4, the effects of stratification must be included. Similarly, ε scaled by the bulk velocity and density differences over the plume displays a clear dependence on Rib, decreasing as Rib approaches Ric. The Kunze et al. ε parameterization is modified to form an expression for the nondimensional dissipation rate that is solely a function of Rib, displaying good agreement with the observations. It is suggested that this formulation is broadly applicable for unstable to marginally unstable stratified shear flows.

Original languageAmerican English
Pages (from-to)2373-2388
Number of pages16
JournalJournal of Physical Oceanography
Volume46
Issue number8
DOIs
StatePublished - 1 Aug 2016

Bibliographical note

Publisher Copyright:
© 2016 American Meteorological Society.

NREL Publication Number

  • NREL/JA-5000-67093

Keywords

  • circulation/dynamics
  • coastal flows
  • estuaries
  • geographic location/entity
  • mixing
  • shear structure/flows
  • turbulence

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